The present invention generally relates to a oneway addressable system such as used in the CATV system and, particularly, to the prevention of viewing of subscription, or pay, television programs by unauthorized subscribers which would result from disconnecting an addressable converter from an AC power outlet.
In the CATV system, in order for the billing to be accurately performed to TV subscribers of subscription television programs, or in order for some of the subscription television programs, which a particular CATV subscriber wishes to view, to be selectively received by a particular CATV subscriber according to their request, an addressable system is hitherto employed. According to the conventional addressable system, a unique address number is allocated to a CATV converter installed in a particular subscriber's home, which converter is at any time controlled by a command transmitted from a broadcasting center as a result of data transmission between the broadcasting center and the CATV converter in the subscriber's home. This addressable system has numerous advantages, some of which is that it is possible to restrict subscribers in arrears, i.e., the subscribers who have failed to pay the charge, from viewing a pay television program transmitted through the CATV system. Also, with respect to the change the particular subscriber has requested in receiving a television program, no service engineer needs to visit the subscriber and the change can be made by using a command from the center to the converter in the subscriber's home. Depending on the data transmission system the center and the CATV converter in the subscriber's home, the addressable system now widely used can be broadly classified into two types: one referred to as a one-way addressable system wherein the data transmission can be carried out only from the center to the CATV converter in the subscriber's home; and the other is referred to as a two-way addressable system wherein the data transmission can be carried out reciprocally between the center and the CATV converter in the subscriber's home.
The one-way addressable system is advantageous in that any existing one-way transmission components such as trunk amplifiers which are used in the conventional community antenna television system can be utilized for the data transmission under the addressable system and that the addressable system can be inexpensively introduced with no need to modify the data transmission system to cope with the two-way system, taking advantage of the existing coaxial network system, and therefore, the one-way addressable system is widely used in the United States of America and some other countries. The prior art construction utilizing this one-way addressable system is shown in FIG. 1 of the accompanying drawings.
Referring to FIG. 1, a broadcasting center arrangement 100 has a host computer 101 which generates a subscriber data through line 102 to a transmission control unit 103. The subscriber data is for controlling a one-way addressable converter 130 installed in a subscriber's home. The transmission control unit 103 performs a format conversion, a data storage and transmission speed conversion and some other functions based on the subscriber data and supplies a control data through line 104 to a data modulator 105. The pattern of the control data will be described later in connection with FIG. 3.
The subscriber data includes: an address number peculiar to a particular subscriber; authorized program information selected according to the subscriber's request; and control information used to disable an addressable converter in the unauthorized subscriber's home. A process, particularly, modulation and RF amplification, which are necessary for the control data to be sent through a coaxial transmission network, is carried out by a data modulator 105 which produces a modulated data signal through line 106. The modulated data signal is applied to a mixer 107 which also receives along line 109 a television signal carrying various pay television programs and usual television programs from an head end 108. At the head end 108, television signals for pay programs are scrambled with the use of a gated sync. supppression technique so that non-subscribers and unauthorized television viewers can not watch the pay television programs.
The television signal on line 109 and the data signal on line 106 are mixed together in mixer 107, and the mixed signal is transmitted through a trunk cable 121. As apparent to those skilled in the art, the data signal transmitted through line 106 has a frequency so selected that it will not overlap with the frequency range of the television signal along line 109.
In data modulator 105, a modulation system based on FSK (Frequency Shift Keying) is used for facilitating the demodulation in the addressable converter. The signals after having been amplified by a trunk amplifier 120, are distributed to the subscriber's television set through a tap-off 122 by way of a drop cable 123.
One-way addressable converter 130 is coupled to each subscriber's television set 140. Addressable converter 130 has a distributor which receives the signal fed through the drop cable 123 and distributes the signal to a converter 133 through line 132 and also to a data demodulator 135 through line 134.
A receiver control data as produced from data demodulator 135 is applied through line 136 to a terminal control unit 137 in which the synchronization, and the error detection of the received control data are performed. Also in the terminal control unit 137, a key scan for the channel selection is carried out together with the detection of the control data. If it is so detected in terminal control unit 137 that an authorized channel or an authorized program is contained in the received data signal, a control signal is applied through line 138 to converter 133 for effecting the channel selection for selecting a frequency of the authorized channel or program. Thus, converter 133 produces a descrambled television signal of the authorized channel or program through line 139 to a television receiver 140, enabling the subscriber to watch the pay television program on the television set 140 using a scramble decoder (not shown).
A further detail of terminal control unit 137 will be described below in connection with FIG. 2. The control data from the data demodulator 135 is taken in a one-chip microprocessor 200 through a serial input port, and then, the serial-parallel conversion is carried out for making data of one character. Although in the example given above, one-chip microprocessor is used in the addressable converter, it is not always limited thereto, but a similar description can apply even where a multi-chip microprocessor is employed. The microprocessor searches synchronization code in the received data and checks the error. If the control data as detected has no error, it is stored in an internal RAM (not shown). Then, comparison is made between the address number contained in the control data with the address number read out from an address ROM 216 in which individual number (ID number) of the particular addressable converter is stored. If these two address numbers coincide with each other, the received control data is deemed as addressed to that particular addressable converter.
One example of a pattern of the control data 104 transmitted from the broadcasting center arrangement 100 to the addressable converter 130 is illustrated in FIG. 3.
If the individual ID number stored in the address ROM 216 and an address number 302 as contained in the control data transmitted from the broadcasting center coincide with each other, microcomputer 200 determines that the control data transmitted from the center is destined to that television receiver with that individual number. Thus, the command data 303 contained in the control data is used in that particular television receiver. In FIG. 3, SYN 301 is provided for indicating the beginning of the control data.
One-chip microcomputer 200 is usually supplied with a DC power from a power circuit (not shown) in the addressable converter through a power source line 207 and power selector 206. The power source line 207 is connected to a detector 213. Detector 213 detects the failure of the primary power supply through the power source line 207, when the line connected to the outlet is disconnected, and produces a power failure signal to microcomputer 200 through line 212 and also produces a control signal through line 209 to power selector 206. Upon receipt of the control signal, power selector 206 is actuated instantaneously to establish an secondary supply power from battery 203 through line 208 to microcomputer 200 and also to timer 210.
In the meantime, upon detection of the power failure signal from line 212, the microcomputer 200 stops its operation and, at the same time, stores various data contained in the RAM in the microcomputer. Thus, during the failure of primary power supply from the power source line 207, an secondary power, such as from battery 203, is used for holding the various data contained in the RAM and also for continuing the time counting by timer 210. The output of timer 210 is connected to microcomputer 200 through line 211 so that the microcomputer is informed of the content of timer 210.
Unlike two-way addressable system, the one-way addressable system may provide data only from the broadcasting center to each subscriber. Thus, it is not possible to detect at the broadcasting center the failure of the primary power supply in the subscribers. Therefore, there may be cases when the subscribers who do not want to pay the fees intentionally disconnect the line from the AC outlet so to as to cause the addressable converter not to recieve any further commands from the broadcasting center. Thus, the command for deauthorizing further program to those subscribers, in response to the failure of paying the fees, will not be received by the subscriber's addressable converter. Thus, such faithless subscribers can continue to receive the programs even after the deauthorize command has been dispatched.
In another case, when the primary power line is disconnected after the subscriber applies to the broadcasting center for changing his tier level, the command for changing the tier level from the broadcasting center may not be received by the addressable converter so that the subscriber continues to receive the programs according to the previous tier level. An extreme example for this case, called churn, may be such that the subscriber first applies for all the programs and, thereafter, cancels the programs but leaving only one program remained as wanted. Then, by disconnecting the addressable converter from the AC outlet, the command for cancelling the programs will not be received by the addressable converter. Thus, even after the cancellation, the subscriber may receive all the programs.
In order to avoid such a piracy in the one-way addressable converter, a timer is provided which counts time while the AC power is not supplied to the addressable converter from the outlet. For example, according to the prior art circuit shown in FIG. 2, upon detection of the failure of power supply through the power source line 207, detector 213 provides the power failure signal through line 212 to the microcomputer 200 which thereupon reads the time as indicated by timer 210. Then, when the power supply through the power source line 207 starts again, detector 213 provides power established signal through line 212 to microcomputer 200, which thereupon reads the time as indicated by timer 210. Microcomputer 200 further calculates a time period in which the power is cut, and compares the calculated time period with a predetermined reference time period. If the calculated time period is greater than the predetermined reference time period, microcomputer 200 is so programmed as to stop its function immediately.
According to the prior art one-way addressable system, a timer which must be actuated during the failure of the primary power supply is necessary, resulting in a high manufacturing cost.
Also, the necessity of the timer eventually calls for the need of an secondary power source, such as a battery, for providing power to the timer while the connection to the primary power source is cut. Usually a backup battery is provided to hold data in RAM until the reestablish of the primary power source, but such a backup battery has a very small capacity sufficient to hold data in RAM. If it is necessary to use the backup battery also for driving the timer, a battery with a greater capacity is necessary, resulting also in a high manufacturing cost.
Furthermore, according to the prior art one-way addressable system, it may be possible for a skilled peson to stop the timer to advance when the connection to the primary power source is cut. This may be accomplished simply by cutting the power supply to the timer.